Light source including an arc tube



June 10, 1958 M. E. MACKSOUD LIGHT SOURCE INCLUDING AN ARC TUBE 2 Sheets-Sheet 1 Filed Dec. 28, 1956 INVENTOR. Mama 5 MIC/(JOUD ATTOB/Vfyy M. E. MACKSOUD LIGHT SOURQE INCLUDING AN ARC TUBE June 10, 1958 2 Sheets-Sheet 2 Filed Dec. 28, 1956 INVENTOR. Mae a f 4440/0000 BY QOJ EDML 2,838,713 Patented June 10, 1958 ice , 2,833,713 LIGHT SOURCE INCLUDING AN ARC TUBE Michel E. Macksoud, New York, N. Y., assignor to Dure- Test Corporation, North Bergen, N. J., a corporation of New York 7 v This invention seeks to improve the efficiency of operation and life of a light sourceconsisting of a combination-of an arc discharge tube and an incandescent filament.

-As is well known in this art, arc discharge tubes used as light sources include an envelope which is an efiicient transmitter of ultra-violet light, as for example quartz or any high silica content glass. When such an arc tube is used in combination with an incandescent filament it has been found that the arc tube envelope gradually deteriorates physically, reducing its transparency to ultraviolet light. This reduction in ultra-violet light transmission is the result of physical deterioration of the arc tube envelope because it is believed the pure quartz crystals of which the envelope is made up, break down, producing a flaky condition in the envelope and inextremc cases, causing its ultimate failure.

It is believed that these conditions result from excessive heating of the quartz envelope, especially when used in combination with incandescent filaments. Deterioration is also caused by faulty ballasts sometimes usedin connection with such combinations where, in addition to the arc discharge tube and incandescent filament, there is present a fluorescent coating. Faulty ballasts are sometimes the source of excessive heat, further contributing to the deterioration of the arc tube envelope. In this disclosure the break down of crystal structure will generally be referred to as devitrific'ation.

Such devitrification is also believed to be caused by the unbalanced electrostatic field which is associated with the usual method of interconnecting the arc tube and the incandescent filament. This unbalanced electrostatic field tends to displace the arc in the arc discharge tube transversely of the central longitudinal axis of the tube, abnormally raising the temperature of the quartz envelope and contributing to the breakdown of its crystalline structure.

A broad object of this invention is to provide in such a combination, means for minimizing devitrification of the quartz or high silica content glass comprising the envelope of the arc discharge tube.

Another object of the invention is to provide an interconnection of the elements of such a light source so as to balance the electrostatic field for reduced potential differences between selected points of the combination to reduce devitrification.

Other and more detailed objects of the invention will be apparent from the following description of the embodiment thereof illustratedin the attached drawings.

In the drawings,

Figure 1 is an elevational view of a light source of the type to which this invention is applicable, showing the main envelope in cross-section;

Figure 2 is a perspective view of this assembly, also with a portion of the envelope broken away for purposes of clarity; and

Figure 3 is a schematic and diagrammatic view of the ferences between the elements thereof.

circuitry for the elements of the light source by means of which the objects of this invention are obtained.

There is coming into extensive use an electric lamp which is a combination of three difierent types of light sources, viz. an arc discharge light source, an incandescent light source and a fluorescent light source, all contributing components of light to the total light output to provide an improved spectrum of useful light. Live tests of these lamps has resulted in the discovery that the envelope of the arc discharge tube which is usually quartz or any high silica content glass, breaks down physically. It is believed that this breaking down which can accurately be defined as devitrification, is the result of subjecting the quartz envelope to the high temperatures normally encountered in such a combination and the potential dif- These factors cause a gradual breaking down of the crystal structure of the arc tube envelope, rendering it less and less transparent to transmission of ultra-violet light as'it ages under these conditions, and in addition actually causing flaking of the envelope and in excessive cases actual failure thereof.

Experience has indicated that thebreaking down of the quartz arc tube envelope is more pronounced at points of excessive temperatures or in fields of high potential difierence. These conditions are encountered whether the lamp is operated face up or face down, and is particularly noticeable if the lamp is operated in a horizontal position with the filament sections above and below the arc tube envelope. These considerations will have more meaning when the structure of the lamp is better understood. 1

Such a lamp is illustrated in the attached drawings. It comprises an outer glass envelope ltlcon'ipose'd of a bulbous portion having an integral seat 14 formed 'therein and an integral neck portion 16 which is provided with the usual re-entrant stem and press 18. The end of the neck portion is provided with the usual screw thread contact base 26 and central contact button 21. The interior of the bulbous portion 12 is provided with a phosphor coating 11 which may be composed of any of the phosphors or mixtures thereof commoniy used in fluorescent lamps.

Mounted on the stem press 18 are a pair of wire supports 22 and 24 which are respectively connected by the lead-in wires 66 and 64 to the contact button 21 and the conductive base 20.

Usually by welding to the support 22 is a wire frame 26 of generally U-shaped form lying vertically along the axis of the envelope 10 with its free ends pointing upwardly. Mounted on the arms of the frame 26 and insulated therefrom are a pair of longitudinally spaced metal plates 28 and 30. These plates are insulated from the arms of the frame 26 by insulating bushings34.

Also mounted on these plates are pairs of bushings 35 positioned in diametrical relation on an axis at right angles to the axis of the bushings 34. Mounted in the bushings 35 are a series of L-shaped wire supports 36 between which, in pairs, extend incandescent filament sections 38 and 40. These filament sections can be of any suitable physical construction and may contain or be coated with coatings containing electron emissi've-materials. Extending between the filament sections arebraces' 42 which include insulators so as not to short circuit them. The filament sections are arranged parallel to the longi tudinal axis of the envelope 10 and are transversely spaced therefrom in diametric relationship.

Lying between the filament sections and supported by the plates 28 and 30 is an arc discharge tube 32 which consists of a quartz or high silica containing glass envelope, as is well known in the lighting industry. As shown in Figure 2, there is positioned at each end of the the electrode 32 of the arc tube 32.

are tube envelope a pair of electron emissive electrodes 32 and 32 which lie on the longitudinal axis of the envelope which is of cylindrical form and of constant diameter. Positioned adjacent one of these electrodes, in the case illustrated electrode 32 is a starting electrode 32.

The support 24 is'connected by a jumper connection 44 to the L-shaped wire filament support 36, connected to one end of the filament section 40. The other end of this filament section is connected to a support 36 which in turn is connected by a jumper 46 to the'electrode 32 of the arc tube.

A resilient support for the upper end of the U-shaped frame 26 is provided and consists of a metal ring 47 with attached resilient cantilever arms 48 shaped to fit into the boss 14 on the envelope 10. The ring of this resilient assembly is welded to the free ends of the U- shaped frame 26 and is connected by a jumper 50 to the L-shaped support 36 for the upper end of the filament sec- 9 thereof is connected by a jumper 54 to one terminal of a resistor 56. Its other terminal 60 is welded to the U- shaped support 26. This resistor is also provided with a stronger physical support in the form of a radial arm 58, which is welded to the frame 26.

Also welded to each side of the frame 26 are a pair of spring arms 62 which are shaped and proportioned to engage the inner wall of the neck 16 to further support the interior assembly on the longitudinal axis of the envelope 10.

While Figures 1 and 2 illustrate very well the electrical interconnection of the elements of the structure, these connections are more simply illustrated diagrammatically in Figure 3. It is clear from this figure that the arc discharge tube is in series with the filament sections. Thus the current enters the circuit through the lead 64 and jumper 54 to the lower end of the filament section 40, its upper end being connected through jumper 46 to The electrode 32 of the arc tube is connected by jumper 52 to the lower end of filament section 38 and its upper end is connected by jumper 50 to the conductor frame 26 which is The subject matter of this invention ditfers from the disclosure in my copending application Serial No. 590,861, filed June 12, 1956, for Electric Lamp, wherein a pair of filament sections are also shown connected in series with the arc discharge tube. In the present application instead of directly connecting the filament sections in series and together endwise with the arc discharge tube, it will be noted that as shown in Figure 3, the current supply is connected to one end of a filament section, the other end being connected to the adjacent end of the arc tube and the other current supply connection being connected directly to the opposite end of the other filament section, the other end of that section being connected to the opposite end of the arc discharge tube.

This arrangement causes a balanced and uniform electrostatic field in which the arc discharge tube lies, as itmust in its physical association with the filament sections.

It appears that since the quartz wall of the arc discharge tube acts as a dielectric between the arc discharge itself and the high potential side of the ballast filament adjacent thereto, the dielectric stress or potential'gradient in the dielectric is the highest on the high potential side of the "ballast filament section, consequently the dielectric hysteresis loss at this side is greater than the loss at the opposite side which is the low potential side. 7 Consequently the quartz on the high potential side of the ballast filament will tend to deteriorate quicker, again resulting in devitrification due to the increased hysteresis losses. Another efiect that has been observed is bestdescribed as electro-osmosis. This tends to allow a trace of mercury compounds and other impurities to diffuse through the quartz wall adjacent to the high potential side of the ballast filament because of electrostatic fields. This electroosmosis characteristic also tends to cause devitrification of the quartz wall.

To state it another way, the maximum potential difference between the high potential end of either filament section is substantially less, that is approximately onehalf potential difierence between the high potential end of the filament if they were directly connected in series as in the related case. The overall result is that devitrification of the envelope of the tube 32 is minimized for the reasons hereinbefo-re explained.

It will be understood that the usual and well known gaseous fillings will be present in the arc discharge tube 32 and the main bulb 18 to insure maximum ultra-violet light production in the case of the former, and efiicient incandescent filament operation in the case of the latter.

In view of the above disclosure it will be apparent to those skilled in the art that the subject matter of this invention is capable of variation in detail, and it is desired, therefore, that the scope of protection afforded hereby be determined by the claims.

What is claimed is:

1. A light source comprising in combination an evacuated bulb having a phosphor coating, a support structure mounted in said bulb, an arc discharge tube secured on said support structure and having a crystalline ultra-violet light transmitting envelope, filament sections on said support structure at opposite sides of and parallel to said envelope, and means comprising energizing circuit connections for said discharge tube and filament sections to create a substantially uniform electrostatic field around said are tube.

2. In the combination of claim 1, said circuit means applying a lower potential between the high potential end of either filament section and said are tube than the operating potential applied to the circuit.

3. In the combination of claim 1, said circuit means connecting said discharge tube and filament sections in series, the arc tube being interposed between said filament sections.

References Cited in the file of this patent UNITED STATES PATENTS 1,617,633 Heany Feb. 15, 1927 2,189,508 Macksoud Feb. 6, 1940 2,369,987 Sperti Feb. 20, 1945 2,524,455 Macksoud Oct. 3, 1950 2,625,670 Embshofi Jan. 13, 1953 FOREIGN PATENTS 886,534 France July 5, 1942 

